JPH0969590A - Silicon nitride circuit substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride circuit substrate where high-strength high-toughness characteristics which a silicon nitride sintered body originally has are utilized, heat conductivity is high and cooling property is high and at the same time heat resistance cycle characteristics can be drastically improved, at the same time packaging property in the assembly process to a semiconductor device is improved. SOLUTION: In a circuit substrate 1 where a circuit layer 4 is joined in one piece to a silicon nitride substrate 2 with a high heat conductivity of 60W/m.K or higher, preferably 90W/m.K or higher, a plurality of semiconductor elements 6 are mounted to the silicon nitride substrate 2 with a high heat conductivity via the circuit layer 4. The circuit layer 4 is formed by the direct junction method, the active metal method, or the metallization method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride circuit board on which a semiconductor element is mounted, and more particularly to a silicon nitride circuit board which can improve heat dissipation characteristics, mechanical strength and heat resistance cycle characteristics and is excellent in mountability.

[0002]

2. Description of the Related Art Conventionally, a conductive metal circuit layer is integrally joined with a brazing material to the surface of a ceramic substrate having excellent insulating properties such as an alumina (Al ₂ O ₃ ) sintered body, A circuit board in which a semiconductor element is mounted at a predetermined position on a circuit layer is widely used.

On the other hand, a ceramic sintered body containing silicon nitride as a main component generally has excellent heat resistance even in a high temperature environment of 1000 ° C. or higher, and also has excellent thermal shock resistance. As a high-temperature structural material that replaces the heat-resistant superalloy described above, it has been tried to be applied to various high-strength heat-resistant parts such as gas turbine parts, engine parts, and steel-making machine parts.

Conventionally, as a composition of a silicon nitride ceramics sintered body, yttrium oxide (Y
₂ O ₃ ), cerium oxide (CeO), calcium oxide (CaO) and other rare earth elements or alkaline earth element oxides are known to be added as sintering aids. The sinterability is enhanced to achieve higher density and higher strength.

A conventional silicon nitride sintered body is formed by adding the above-mentioned sintering aid to a silicon nitride raw material powder, and molding the obtained molded body at a temperature of about 1600 to 2000 ° C. in a firing furnace. It is manufactured by a manufacturing method in which after firing for a time, the furnace is cooled, and the resulting sintered body is ground and polished.

[0006]

However, although the silicon nitride sintered body manufactured by the above-mentioned conventional method has excellent mechanical strength such as toughness, it is different from other aluminum nitrides in terms of thermal conductivity. AlN) sintered body, beryllium oxide (BeO) sintered body, silicon carbide (SiC) sintered body, etc. are significantly lower than those in electronic materials such as semiconductor circuit boards that require heat dissipation. Has not been put to practical use, and has a drawback that its application range is narrow.

On the other hand, the aluminum nitride sintered body has the characteristics of high thermal conductivity and low thermal expansion coefficient as compared with other ceramics sintered bodies, and therefore, higher speed, higher output, multi-functionality and larger size are progressing. It is widely used as a circuit board component for mounting a semiconductor element (chip) and a package material. However, since AlN sintered bodies have not been obtained that are sufficiently satisfactory in terms of mechanical strength, damage may occur during the circuit board mounting process, or the mounting process may become complicated, and the manufacturing efficiency of semiconductor devices may decrease. There was a problem to do.

That is, when a circuit board whose main constituent material is a ceramics substrate such as the above aluminum nitride sintered body substrate or aluminum oxide sintered body substrate is fixed to the mounting boat by screwing or the like in the assembly process, In some cases, the circuit board may be damaged by a slight deformation due to the pressing force of or and the impact at the time of handling, and the manufacturing yield of the semiconductor device may be significantly reduced.

Further, since the strength of the circuit board is small, it is difficult to form a large circuit board, and a small circuit board having one semiconductor element mounted on the upper surface of a small ceramic board has been widely used. Therefore, when assembling the semiconductor device, many circuit boards are individually incorporated into the device body according to the number of functions required, which complicates the mounting process and reduces the manufacturing efficiency of the semiconductor device. There was a point.

Further, in the circuit board formed by integrally bonding the metal circuit layer and the semiconductor element on the surface of the aluminum nitride substrate as described above, the mechanical strength and toughness of the aluminum nitride substrate itself are insufficient, so that the semiconductor Due to repeated thermal cycles associated with the operation of the element, cracks are likely to occur in the aluminum nitride substrate in the vicinity of the joint portion of the metal circuit layer, and the heat cycle characteristics and reliability are low.

The present invention has been made in order to meet the above-mentioned demands, and utilizes the high-strength and high-toughness characteristics originally possessed by a silicon nitride sintered body, and further has high thermal conductivity and excellent heat dissipation. At the same time, it is an object of the present invention to provide a silicon nitride circuit board which can greatly improve the heat-resistant cycle characteristics while improving the mountability in the process of assembling the semiconductor device.

[0012]

In order to achieve the above object, the present inventor has researched a substrate material which does not deteriorate the heat dissipation (thermal conductivity) of a circuit board and satisfies both strength and toughness values. At the same time, we conducted extensive research on measures to prevent tightening cracks that occur in the assembly process of circuit boards and cracks that occur when heat cycles are applied and improve mountability. As a result, regarding the substrate material, by appropriately controlling the composition and manufacturing conditions, a silicon nitride sintered body having an unprecedented high thermal conductivity was obtained, and this silicon nitride sintered body was used. To form a large-sized circuit board and to integrally form a circuit layer on the surface of the circuit board and to mount a plurality of semiconductor elements into a large-sized circuit board, effectively prevent the circuit board from tightening cracks in the assembly process. The inventors have completed the present invention by finding that it can be reduced, the heat resistance cycle characteristics can be greatly improved, and the circuit board mountability in the assembly process can be greatly improved.

That is, the inventors of the present invention have studied the type of silicon nitride powder, the type and amount of sintering aids and additives, and the sintering conditions that have been conventionally used, and found that the conventional silicon nitride sintered body Has developed a silicon nitride sintered body having a high thermal conductivity which is more than twice as high as that of. Further, using this silicon nitride sintered body as a substrate material, a metal circuit layer having conductivity is integrally bonded to the surface thereof, and a plurality of semiconductor elements are mounted on the same substrate to form a large circuit board. It was confirmed by an experiment that even when manufactured, a silicon nitride circuit board satisfying all of mechanical strength, toughness value, heat cycle characteristics, heat dissipation and mountability can be obtained.

Specifically, a raw material mixture obtained by adding a predetermined amount of a rare earth element oxide or the like to fine and highly pure silicon nitride powder is molded and degreased, and the obtained molded body is heated at a predetermined temperature for a certain period of time. After carrying out densification sintering while holding, gradually cooling at a cooling rate below a predetermined value, and when the resulting sintered body was ground and polished, the thermal conductivity of the conventional silicon nitride sintered body was increased. It has been found that a silicon nitride sintered body having a high strength and a high toughness, which is significantly improved by more than twice, specifically, 60 W / m · K or more, can be obtained, and a new one satisfying both heat dissipation characteristics and strength characteristics. Developed a new silicon nitride material. It has been found that when this silicon nitride material is applied to a board material of a circuit board, excellent heat dissipation characteristics, durability, heat cycle characteristics, and mountability can be simultaneously improved.

A glass phase (amorphous phase) in the grain boundary phase is obtained by using a high-purity silicon nitride raw material powder having a reduced content of oxygen and impurity cation elements and sintering the powder under the above conditions. The formation of the rare earth element oxide alone can be effectively suppressed by controlling the ratio of the crystalline compound phase in the grain boundary phase to 20% or more (to the entire grain boundary phase), and more preferably 50% or more. 60 W / mK or more, more preferably 80 W / mK
It was found that a silicon nitride sintered body substrate having a high thermal conductivity of K or higher can be obtained.

Further, conventionally, when the heating power source of the firing furnace was turned off after the sintering operation and the sintered body was cooled in the furnace, the cooling rate was as rapid as 400 to 800 ° C./hour. According to the experiments by the inventor, the cooling rate is 10
By controlling the temperature slowly to 0 ° C or lower, the grain boundary phase of the silicon nitride sintered body structure changes from an amorphous state to a phase containing a crystalline phase, and high strength characteristics and high heat transfer characteristics are simultaneously achieved. It turned out that

A part of the high thermal conductivity silicon nitride sintered body itself has already been applied for a patent by the present inventor, and further applied in Japanese Patent Application Laid-Open Nos. 6-135771 and 7-48174. It has been published. The silicon nitride sintered bodies described in these patent applications convert the rare earth elements into oxides of 2.0 to
It contains 7.5% by weight. However, as a result of further improvement research conducted by the present inventor, when the contained rare earth element exceeds 7.5% by weight in terms of oxide, the sintered body has a higher thermal conductivity, and the sintered body has a higher thermal conductivity. The inventors of the present invention have completed the invention by discovering that the connectivity is also good. In particular, the effect is remarkable when the rare earth element is a lanthanoid series element. By the way, even when the ratio of the crystal compound phase in the grain boundary phase to the whole grain boundary phase is 60 to 70%, the sintered body can achieve a high thermal conductivity of 110 to 120 W / m · K or more.

As described above, the silicon nitride sintered body satisfying both the high strength property and the high heat transfer property is used as the substrate material, and the metal circuit layer is integrally bonded to the surface of the substrate material to form the circuit board. It has been found that the toughness and thermal conductivity of the entire board can be improved, and in particular, the occurrence of tightening cracks in the circuit board assembly process and cracks due to the addition of heat cycles can be effectively prevented. In particular, even when a large-sized substrate is created using the above silicon nitride sintered body, a circuit layer is integrally formed on the surface of the substrate, and a plurality of semiconductor elements are mounted to form a large-sized circuit board, It has been found that tightening cracks are less likely to occur and the manufacturing yield is improved, and at the same time, the circuit board mounting process is simplified and the semiconductor device manufacturing efficiency can be significantly improved.

The present invention has been completed based on the above findings. That is, in the silicon nitride circuit board according to the present invention, the rare earth element is converted into oxide in an amount of 2.0 to 17.5% by weight, and Li, Na, K and F as impurity cation elements are used.
e, Ca, Mg, Sr, Ba, Mn, B total 0.3
A circuit board in which a circuit layer is bonded to a high thermal conductivity silicon nitride substrate containing less than or equal to wt% and having a thermal conductivity of 60 W / mK or more, and a circuit layer is provided on the high thermal conductivity silicon nitride substrate. And a plurality of semiconductor elements are mounted.

The silicon nitride circuit board according to the present invention comprises:
2.0 to 17.5 wt% of rare earth elements converted to oxides, Li, Na, K, F as impurity cation elements
e, Ca, Mg, Sr, Ba, Mn, B total 0.3
It is contained in an amount of up to 20% by weight, is composed of a silicon nitride crystal and a grain boundary phase, and the ratio of the crystal compound phase in the grain boundary phase to the entire grain boundary phase is 20% or more and the thermal conductivity is 60 W /
A circuit board in which a circuit layer is bonded to a high thermal conductivity silicon nitride substrate of m · K or more, wherein a plurality of semiconductor elements are mounted on the high thermal conductivity silicon nitride substrate via the circuit layer. To do.

Further, the high thermal conductivity silicon nitride substrate contains a rare earth element in an amount of 2.0 to 17.5 wt% in terms of oxide, and is composed of a silicon nitride crystal and a grain boundary phase, and in the grain boundary phase. It may be formed from a silicon nitride sintered body in which the ratio of the crystalline compound phase to the entire grain boundary phase is 50% or more.

It is preferable that the three-point bending strength of the high thermal conductivity silicon nitride substrate is 650 MPa or more. Further, the thickness of the silicon nitride substrate having high thermal conductivity may be set to be twice the thickness of the circuit layer or less.

It is further preferable that the high thermal conductivity silicon nitride substrate has a thermal conductivity of 90 W / m · K or more. Alternatively, the circuit layer may be a metal circuit board, and the metal circuit board may be bonded onto a high thermal conductivity silicon nitride substrate having an oxide layer on its surface. Further, the circuit layer is a metal circuit board, and the metal circuit board has a high thermal conductivity silicon nitride substrate through an active metal brazing material layer containing at least one active metal selected from Ti, Zr, Hf and Nb. It may be configured to be bonded on top. The circuit layer may also be composed of a refractory metallized layer.

Further, it is particularly preferable that a lanthanoid series element is contained as the rare earth element in the above silicon nitride substrate in order to improve the thermal conductivity.

Further, aluminum nitride or alumina may be added in an amount of 1.0% by weight or less to form a silicon nitride substrate. Further, 1.0% by weight or less of alumina and 1.0% by weight or less of aluminum nitride may be used together.

The high thermal conductivity silicon nitride sintered body used in the present invention is made of Ti, Zr, Hf, V, Nb and T.
It is preferable that at least one selected from the group consisting of a, Cr, Mo, and W is contained in an amount of 0.1 to 3.0 wt% in terms of oxide. This Ti, Zr, Hf, V, Nb,
At least one selected from the group consisting of Ta, Cr, Mo, and W can be contained by adding it to the silicon nitride raw material powder as an oxide, a carbide, a nitride, a silicide, or a boride.

Further, in the method for producing a high thermal conductivity silicon nitride sintered body used in the present invention, oxygen is 1.7 wt% or less, and Li, Na, K, Fe and C as impurity cation elements are used.
0.3% by weight of a, Mg, Sr, Ba, Mn, B in total
Hereinafter, the content of the α-phase type silicon nitride is 90% by weight or more, and the raw material powder of silicon nitride having an average particle size of 1.0 μm or less is 2.0 to 17.5% by weight in terms of the oxide of the rare earth element. If necessary, at least one of alumina and aluminum nitride is added in an amount of 1.0% by weight or less to form a raw material mixture to prepare a green body, and the obtained green body is degreased at a temperature of 180.
Atmospheric pressure sintering at 0 to 2100 ° C., the cooling rate of the sintered body from the above sintering temperature to the temperature at which the liquid phase formed during sintering by the above rare earth element solidifies is 100 ° C./hour.
It is characterized in that it is gradually cooled as follows. The obtained sintered body is ground and polished into a predetermined shape to manufacture the high thermal conductivity silicon nitride substrate used in the present invention.

In the above manufacturing method, it is preferable to add 1.0% by weight or less of at least one of alumina and aluminum nitride to the silicon nitride powder.

In addition to silicon nitride powder, Ti, Z
oxides of r, Hf, V, Nb, Ta, Cr, Mo, W,
It is preferable to add 0.1 to 3.0% by weight of at least one selected from the group consisting of carbides, nitrides, silicides and borides.

According to the above manufacturing method, a grain boundary phase containing a rare earth element or the like is formed in the silicon nitride crystal structure, the porosity is 2.5% or less, the thermal conductivity is 60 W / m · K or more, and It is possible to obtain a silicon nitride sintered body having a point bending strength of 650 MPa or more at room temperature, which is excellent in both mechanical properties and heat conduction properties.

The silicon nitride powder which is the main component of the high thermal conductivity silicon nitride substrate used in the present invention has an oxygen content of 1.7 wt% in consideration of sinterability, strength and thermal conductivity. % Or less, preferably 0.5 to 1.5% by weight,
Li, Na, K, Fe, Mg, Ca, Sr, Ba, M
The total content of impurity cation elements such as n and B is 0.3.
It contains 90% by weight or more, preferably 93% by weight or more, of α-phase type silicon nitride suppressed to a weight% or less, preferably 0.2% by weight or less, and has an average particle size of 1.0 μm or less, preferably 0. Fine silicon nitride powder of about 4 to 0.8 μm can be used.

By using a fine raw material powder having an average particle size of 1.0 μm or less, it is possible to form a dense sintered body having a porosity of 2.5% or less even with a small amount of a sintering aid. It is also possible to reduce the risk of the sintering aid impairing the heat conduction characteristics.

Li, Na, K, Fe, Ca, Mg,
Impurity cation elements of Sr, Ba, Mn, and B are substances that impede thermal conductivity. Therefore, in order to ensure a thermal conductivity of 60 W / m · K or more, the content of the impurity cation elements is It can be achieved by setting the total to 0.3% by weight or less. Particularly, for the same reason, the total content of the above-mentioned impurity cation elements is 0.2% by weight or less,
More preferred. The silicon nitride powder used for obtaining the usual silicon nitride sintered body is particularly Fe, C.
Since a and Mg are contained in relatively large amounts, Fe and C
The total amount of a and Mg is a measure of the total content of the above impurity cation elements.

Further, by using a silicon nitride raw material powder containing 90% by weight or more of α-phase type silicon nitride, which is superior in sinterability as compared with the β-phase type, a high density sintered body is manufactured. can do.

The rare earth elements added to the silicon nitride raw material powder as a sintering aid include Ho, Er, Yb, Y,
Depending on the oxide such as La, Sc, Pr, Ce, Nd, Dy, Sm, Gd or the sintering operation, these oxide substances may be used alone or in combination of two or more kinds. Good, but especially holmium oxide (Ho ₂ O
₃ ) and erbium oxide (Er ₂ O ₃ ) are preferred.

In particular, by using lanthanoid series elements Ho, Er and Yb as the rare earth element, the sinterability or the high thermal conductivity is improved, and the firing is sufficiently dense even in the low temperature region of about 1850 ° C. A union is obtained. Therefore, the effect of reducing the equipment cost and running cost of the firing apparatus can be obtained. These sintering aids are
It reacts with the silicon nitride raw material powder to form a liquid phase and functions as a sintering accelerator.

The amount of the above-mentioned sintering aid added is in the range of 2.0 to 17.5% by weight based on the raw material powder in terms of oxide.
If the added amount is less than 2.0% by weight, the densification of the sintered body is insufficient, and particularly when the rare earth element is an element having a large atomic weight such as a lanthanoid element, the strength is relatively low. A sintered body having a relatively low thermal conductivity is formed. on the other hand,
If the addition amount exceeds 17.5% by weight, an excessive amount of grain boundary phase is generated, and thermal conductivity and strength start to decrease, so the above range is set. Particularly, for the same reason, it is desirable that the amount is 4 to 15% by weight.

Further, Ti, Zr, Hf, V, Nb and T used as other selective addition components in the above manufacturing method.
The oxides, carbides, nitrides, suicides, and borides of a, Cr, Mo, and W promote the function of the above-mentioned rare earth element sintering promoter and, at the same time, function as a dispersion strengthener in the crystal structure of Si ₃ It improves the mechanical strength of the N ₄ sintered body, and a compound of Hf and Ti is particularly preferable. If the addition amount of these compounds is less than 0.1% by weight, the effect of addition is insufficient, while if it exceeds 3.0% by weight, the thermal conductivity, mechanical strength, and electrical breakdown Since the strength decreases, the addition amount is set to the range of 0.1 to 3.0% by weight. In particular, it is desirable that the content be 0.2 to 2% by weight.

The compounds such as Ti, Zr, and Hf also function as a light-shielding agent for coloring the silicon nitride sintered body in a blackish color to impart opacity. Therefore, particularly when manufacturing a circuit board on which an integrated circuit or the like is likely to malfunction due to light, it is desirable to appropriately add the compound such as Ti to obtain a silicon nitride substrate having an excellent light shielding property.

Further, in the above-mentioned manufacturing method, alumina (Al ₂ O ₃ ) as another optional additive component plays a role of promoting the function of the sintering promoter of the rare earth element, and particularly the pressure It exhibits a remarkable effect when sintering is performed. When the added amount of Al ₂ O ₃ is less than 0.1% by weight, it is necessary to sinter at a higher temperature, while when the added amount exceeds 1.0% by weight, an excessive amount of grain boundary is used. A phase is generated or a solid solution begins to form a solid solution in silicon nitride and the thermal conductivity is lowered. Therefore, the addition amount is 1% by weight or less, preferably 0.1 to 0.75% by weight.
In particular, in order to secure good performances in both strength and thermal conductivity, it is desirable that the addition amount be in the range of 0.1 to 0.5% by weight.

When used in combination with AlN, which will be described later, it is desirable that the total addition amount be 1.0% by weight or less.

Further, aluminum nitride (AlN) as another additive component suppresses the evaporation of silicon nitride in the sintering process and also promotes the function of the above rare earth element as a sintering accelerator. Is.

When the amount of AlN added is less than 0.1% by weight (less than 0.05% by weight when used in combination with alumina), sintering at a higher temperature is required.
If the amount exceeds 0% by weight, an excessive amount of grain boundary phase is generated or begins to form a solid solution in silicon nitride, and the thermal conductivity decreases, so the addition amount is 0.1 to 1.0. The range is wt%. In particular, in order to secure good performances in terms of sinterability, strength, and thermal conductivity, it is desirable that the addition amount be in the range of 0.1 to 0.5% by weight. When used in combination with Al ₂ O ₃ , the addition amount of AlN is 0.05 to 0.5% by weight.
Is preferred.

The porosity of the sintered body has a great influence on the thermal conductivity and the strength, so that the sintered body is manufactured so as to have a porosity of 2.5% or less. If the porosity exceeds 2.5%, it will hinder heat conduction,
The thermal conductivity of the sintered body decreases and the strength of the sintered body also decreases.

The silicon nitride sintered body is structurally composed of a silicon nitride crystal and a grain boundary phase. The proportion of the crystalline compound phase in the grain boundary phase has a great influence on the thermal conductivity of the sintered body. However, in the silicon nitride sintered body used in the present invention, it is necessary to make it 20% or more of the grain boundary phase, more preferably 50% or more of the crystal phase. This is because if the crystal phase is less than 20%, it is not possible to obtain a sintered body having excellent heat dissipation characteristics such as a thermal conductivity of 60 W / m · K or more and excellent high temperature strength.

Further, as described above, the porosity of the silicon nitride sintered body is set to 2.5% or less, and 20% or more of the grain boundary phase formed in the silicon nitride crystal structure is occupied by the crystal phase. A silicon nitride compact at a temperature of 1800-210.
It is important to perform pressure sintering at 0 ° C. for about 2 to 10 hours and gradually cool the sintered body immediately after the completion of the sintering operation to 100 ° C. or less per hour.

If the sintering temperature is less than 1800 ° C., the densification of the sintered body will be insufficient and the porosity will be 2.5 vol% or more, resulting in a decrease in both mechanical strength and thermal conductivity. On the other hand, if the sintering temperature exceeds 2100 ° C., the silicon nitride component itself tends to evaporate and decompose. Not especially pressure sintering,
When pressureless sintering is carried out, decomposition vaporization of silicon nitride begins at around 1800 ° C.

The cooling rate of the sintered body immediately after the completion of the above-mentioned sintering operation is an important control factor for crystallizing the grain boundary phase, and when the cooling rate is higher than 100 ° C./hour, rapid cooling is performed. The grain boundary phase of the sintered body structure becomes amorphous (glass phase), the liquid phase generated in the sintered body occupies less than 20% of the grain boundary phase as a crystal phase, and the strength and thermal conductivity are Both will decrease.

The temperature range in which the cooling rate should be strictly adjusted is a temperature range from a predetermined sintering temperature (1800 to 2100 ° C.) to the solidification of the liquid phase produced by the reaction of the above-mentioned sintering aid. Is enough. By the way, the liquidus freezing point when the above-mentioned sintering aid is used is approximately 1600 to 15
It is about 00 ° C. The cooling rate of the sintered body from at least the sintering temperature to the liquidus solidification temperature is set to 10 per hour.
0 ° C or lower, preferably 50 ° C or lower, more preferably 2
By controlling the temperature to 5 ° C or lower, 20% or more of the grain boundary phase,
Particularly preferably, 50% or more becomes a crystalline phase, and a sintered body excellent in both thermal conductivity and mechanical strength can be obtained.

The silicon nitride substrate used in the present invention is manufactured through the following processes, for example. That is, with respect to the fine silicon nitride powder having a predetermined fine particle diameter and a small amount of impurities, a predetermined amount of a sintering aid, an organic binder, and other necessary additives and, if necessary, Al ₂ O. _A raw material mixture is prepared by adding ₃ , ₃ , AlN, Ti compounds and the like, and then the obtained raw material mixture is molded to obtain a molded product having a predetermined shape. As a forming method of the raw material mixture, a general-purpose die pressing method, a sheet forming method such as a doctor blade method, or the like can be applied. Following the above molding operation, the molded body is heated in a non-oxidizing atmosphere at a temperature of 600 to 800 ° C. or in air at a temperature of 400 to 500 ° C. for 1 to 2 hours,
The organic binder component added in advance is sufficiently removed and degreased. Next, the degreased molded body is subjected to 1800 in an atmosphere of an inert gas such as nitrogen gas, hydrogen gas or argon gas.
Atmosphere pressure sintering is performed at a temperature of 2100 ° C. for a predetermined time.

The silicon nitride sintered body produced by the above production method has a porosity of 2.5% or less and 60 W / m · K (25
(° C) or more, further 90 W / mK or more, and three-point bending strength of 650 MPa or more at room temperature, which is excellent in mechanical properties.

It is to be noted that a silicon nitride-based sintered body obtained by adding SiC or the like having high thermal conductivity to silicon nitride having low thermal conductivity so that the thermal conductivity of the whole sintered body is 60 W / mK or more is obtained. It is not included in the scope of the invention. However, the thermal conductivity is 60
In the case of a silicon nitride-based sintered body in which a highly heat-conductive SiC or the like is combined with a silicon nitride sintered body having a W / m · K or more,
It goes without saying that as long as the thermal conductivity of the silicon nitride sintered body itself is 60 W / m · K or more, it falls within the scope of the present invention.

The thickness of the high thermal conductivity silicon nitride substrate made of the above silicon nitride sintered body is set to various thicknesses according to the required characteristics when used as a circuit board. By making the thickness twice or less, the substrate itself can be thinned, and the heat dissipation as a circuit board can be improved in the substrate having a constant thermal conductivity. When the thickness of the silicon nitride substrate exceeds twice the thickness of the circuit layer, the thickness of the entire circuit substrate increases and the thermal resistance increases. The specific thickness of the silicon nitride substrate is in the range of 0.25 to 0.8 mm. In particular, by setting the thickness of this silicon nitride substrate to 0.5 mm or less, the thickness of the entire circuit board can be reduced,
The thermal resistance difference between the upper and lower surfaces of the circuit board can be more effectively reduced, and the heat dissipation of the entire circuit board can be further improved.

The silicon nitride circuit board according to the present invention has the high thermal conductivity silicon nitride substrate manufactured as described above,
It is manufactured by integrally bonding conductive circuit layers and mounting a plurality of semiconductor elements via the circuit layers.

The method of forming and joining the circuit layer is not particularly limited, and a direct joining method, an active metal method, a metallizing method, or the like described below can be applied.

In the direct bonding method, an oxide layer having a thickness of about 0.5 to 10 μm is formed on the surface of a high thermal conductivity silicon nitride substrate, and a metal circuit board to be a circuit layer is formed through this oxide layer. This is a method of directly bonding to the silicon nitride substrate. Here, the metal circuit board is directly and integrally bonded to the surface of the silicon nitride substrate without using a bonding agent such as a brazing material. That is, a eutectic compound of the components of the metal circuit board and the substrate component is generated by heating, and the two members are joined using this eutectic compound as a joining agent. Note that this direct bonding method can be applied only to oxide-based ceramics such as Al ₂ O ₃ , and even if it is directly applied to a silicon nitride substrate, it has low wettability to the substrate, so sufficient bonding strength of a metal circuit board is obtained. Can't get

Therefore, it is necessary to previously form an oxide layer on the surface of the silicon nitride substrate to enhance the wettability with respect to the substrate. This oxide layer is formed on the silicon nitride substrate having high thermal conductivity at a temperature of about 1000 to 1400 ° C. in an oxidizing atmosphere such as air.
Formed by heating for ~ 15 hours. When the thickness of the oxide layer is less than 0.5 μm, the effect of improving the wettability is small, but even if it is set to exceed 10 μm, the improving effect is saturated and the thermal conductivity is likely to decrease. Therefore, the thickness of the oxide layer is in the range of 0.5 to 10 μm, more preferably 1 to 5 μm.

Although the oxide layer is initially composed only of SiO ₂ , which is an oxide of the Si ₃ N ₄ substrate component, during the bonding operation of the metal circuit board by heating, the Si ₃ N ₄ substrate has a sintering aid. As a result of the rare earth element oxide added as the agent diffusing and moving toward the oxide layer, the rare earth oxide is concentrated in the oxide layer. For example, as a sintering aid, Y ₂
When O ₃ is used, the oxide layer after the heat bonding operation is Y
Comes to be composed of SiO ₂ -Y ₂ O ₃ compound such yttria silicate containing about a ₂ O ₃ 1 to 20% by weight.

As a metal constituting the metal circuit board, a eutectic compound with a substrate component such as a simple substance of copper, aluminum, iron, nickel, chromium, silver, molybdenum, cobalt, or an alloy thereof is formed and directly contacted. There is no particular limitation as long as it is a metal to which legality can be applied, but copper, aluminum or an alloy thereof is particularly preferable from the viewpoint of conductivity and cost.

The thickness of the metal circuit board (circuit layer) is determined in consideration of the current-carrying capacity and the like, but the thickness of the silicon nitride substrate is set in the range of 0.25 to 0.8 mm, while the metal circuit board is formed. When the thickness of the plate is set in the range of 0.2 to 0.3 mm and the two are combined, the influence of deformation due to the difference in thermal expansion becomes less likely.

When the metal circuit board is a copper circuit board, the joining operation is carried out as follows. That is, a copper circuit board is placed in contact with a predetermined position on the surface of a silicon nitride substrate having a high thermal conductivity on which an oxide layer is formed, and is pressed toward the substrate at a temperature lower than the melting point (1083 ° C.) of copper and −
The copper circuit board is directly bonded to the surface of the high thermal conductivity silicon nitride substrate by heating it to a temperature higher than the eutectic temperature of copper oxide (1065 ° C.) and using the generated Cu—O eutectic compound liquid phase as a bonding agent. This direct bonding method is a so-called copper direct bonding method (DBC: Dire
ct Bonding Copper method). Further, a plurality of semiconductor elements (Si-chips) are provided at predetermined positions on the copper circuit board directly bonded.
By soldering and mounting the Si according to the present invention.
₃ N ₄ circuit boards are manufactured.

On the other hand, when the metal circuit board is an aluminum circuit board, the Al circuit board is heated to a temperature higher than the eutectic temperature of aluminum-silicon while pressing the Al circuit board against the surface of the Si ₃ N ₄ substrate, and the generated Al- Al using Si eutectic compound as a bonding agent
The circuit board is bonded directly to the Si ₃ N ₄ substrate surface. Then, a plurality of semiconductor elements are solder-bonded and mounted at predetermined positions on the Al circuit board which is directly bonded to the Si of the present invention.
₃ N ₄ circuit boards are manufactured.

As described above, the metal circuit board is directly bonded to the surface of the Si ₃ N ₄ substrate by using the direct bonding method, and further, a plurality of semiconductor elements are mounted on the metal circuit board to form Si _{3 according} to the present invention. According to N ₄ circuit board, the metal circuit plate and the Si ₃ N
_{4 Since} there is no inclusion such as adhesive or brazing material between the board and the board, the heat resistance between the two is small, and the heat generated by the semiconductor element mounted on the metal circuit board is quickly dissipated outside the system. It is possible.

Next, a method of joining circuit layers by the active metal method will be described.

In the active metal method, an Ag-Cu-Ti-based brazing material containing at least one active metal selected from Ti, Zr, Hf and Nb and having an appropriate composition ratio is applied to the surface of the silicon nitride substrate. An active metal brazing material layer having a thickness of about 20 μm is formed, and a metal circuit board such as a copper circuit board is joined via the brazing material layer. The active metal has an effect of improving the wettability of the brazing material with respect to the substrate and increasing the bonding strength. As a specific example of the active metal brazing material, a brazing material composition in which the active metal is 1 to 10% by weight, Cu is 15 to 35%, and the balance is substantially Ag is preferable. The active metal brazing material layer is formed by a method such as screen-printing a bonding composition paste prepared by dispersing the brazing material composition in an organic solvent on the surface of the silicon nitride substrate.

Then, in a state where a metal circuit board to be a circuit layer is placed in contact with the screen-printed active metal brazing material layer, in vacuum or in an inert gas atmosphere, for example, Ag--
By heating to a temperature not lower than the Cu eutectic temperature (780 ° C.) and not higher than the melting point of the metal circuit board (1083 ° C. in the case of copper), the metal circuit board is exposed to the active metal brazing material layer through the silicon nitride substrate. Is integrally joined to.

Next, a method of forming a circuit layer by the metallizing method will be described. In the metallization method, for example, molybdenum (M
o) or a refractory metal such as tungsten (W) and a metallized composition mainly containing Ti or a compound thereof are baked on the surface of the silicon nitride substrate to form a refractory metal metallized layer as a circuit layer having a thickness of about 15 μm. Is a method of forming.
When a circuit layer is formed by this metallizing method,
The surface of the metallized layer is made of Ni or Au and has a thickness of 3 to
It is preferable to form a metal plating layer having a thickness of about 5 μm.
By forming this metal plating layer, the surface smoothness of the metallized layer is improved, the adhesion with the semiconductor element is further improved, and the solder wettability is improved, so the bonding strength of the semiconductor element using solder is improved. Can be increased.

According to the silicon nitride circuit board having the above structure, in addition to the high-strength and toughness characteristics originally possessed by the silicon nitride sintered body, the high-thermal-conductivity silicon nitride board in which the thermal conductivity is greatly improved is provided. A circuit layer is integrally bonded to the surface, and a plurality of semiconductor elements are mounted on the surface. Therefore,
Even when a circuit board is formed in a large size for mounting a plurality of elements, the toughness value is high, so that a large maximum deflection amount can be secured. For this reason, the circuit board does not suffer from cracking in the assembly process, and semiconductor devices using the circuit board can be mass-produced with a high manufacturing yield.

Further, since a plurality of semiconductor elements are mounted on the surface of a single silicon nitride substrate to form a circuit board, compared with the conventional case where a circuit board is formed for each semiconductor element, It is possible to reduce the total number of circuit boards, simplify the circuit board mounting process, and improve the manufacturing efficiency of semiconductor devices.

Since the toughness value of the silicon nitride substrate is high,
It is possible to provide a semiconductor device in which cracks are less likely to occur in a substrate due to heat cycle, heat cycle characteristics are remarkably improved, and durability and reliability are excellent.

Furthermore, since a silicon nitride substrate having a high thermal conductivity, which has not been achieved in the past, is used, the thermal resistance characteristics of the semiconductor device can be improved even when a semiconductor device for high output and high integration is mounted. Shows excellent heat dissipation with little deterioration.

In particular, since the silicon nitride substrate itself is excellent in mechanical strength, when the required mechanical strength characteristics are kept constant, the substrate thickness can be made larger than that when other ceramic substrates are used. It becomes possible to reduce. Since the substrate thickness can be reduced, the thermal resistance value can be made smaller,
The heat dissipation characteristics can be further improved. Further, since it is possible to sufficiently meet the required mechanical characteristics even with a substrate thinner than before, it is possible to mount the circuit board at a high density and further downsize the semiconductor device.

[0073]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be specifically described with reference to the following examples.

Examples 1 to 3 1.3 wt% oxygen, Li as the impurity cation element,
Containing 0.15 wt% of Na, K, Fe, Ca, Mg, Sr, Ba, Mn and B in total, and 97% of α-phase type silicon nitride
With respect to the average particle size silicon nitride material powder of 0.55μm comprising, an average particle size of 0.7μm as a sintering aid Y ₂ O
₃ (yttrium oxide) powder 5% by weight, average particle size 0.5
1.0 wt% of Al ₂ O ₃ (alumina) powder of μm was added, wet-mixed in ethyl alcohol for 24 hours, and then dried to prepare a raw material powder mixture. Next, a predetermined amount of an organic binder was added to the obtained raw material powder mixture and uniformly mixed, and then press-molded at a molding pressure of 1000 kg / cm ² ,
A large number of molded products having a length of 80 mm, a width of 50 mm and a thickness of 1 to 5 mm were manufactured. Next, the obtained molded body was degreased in an atmosphere gas at 700 ° C. for 2 hours, and then the degreased body was held in a nitrogen gas atmosphere at 7.5 atm at 1900 ° C. for 6 hours to perform densification sintering. After that, the cooling rate of the sintered body was 50 ° C. until the temperature inside the sintering furnace dropped to 1500 ° C. by controlling the amount of electricity supplied to the heating device attached to the sintering furnace.
/ Hr was adjusted to cool the sintered body, and each of the obtained sintered bodies was polished to obtain a thermal conductivity k of 92.
W / mK, thickness 0.4mm, 0.6mm, 0.8
mm silicon nitride substrates for Examples 1-3 were prepared.

Next, as shown in FIG. 1, each silicon nitride substrate 2
30 wt% Ag-65% Cu-5% Ti brazing filler metal is screen-printed on the portion where the front surface circuit layer is formed and the rear portion where the copper plate is joined, and the active metal brazing filler metal layers 7 a and 7 b having a thickness of 20 μm are dried. Was formed. At a predetermined position on the active metal brazing material layers 7a and 7b, a thickness of oxygen-free copper of 0.3
The copper circuit board 4 having a thickness of 0.25 mm and the back copper plate 5 having a thickness of 0.25 mm were placed in contact with each other, and held in vacuum at a temperature of 850 ° C. for 10 minutes to form a bonded body. Next, a predetermined circuit pattern (circuit layer) was formed by etching each bonded body.
Further, the semiconductor elements 6 were solder-bonded to the central portions of the copper circuit boards 4 at two locations to manufacture a large number of silicon nitride circuit boards 1 according to Examples 1 to 3.

Comparative Example Other than using the silicon nitride substrate used in Examples 1 to 3, an aluminum nitride (AlN) substrate having a thermal conductivity k of 70 W / mK and a thickness of 0.8 mm was used. Is Example 1
In the same manner as in No. 3, a copper circuit board and a back copper plate were integrally joined to the surface of the board by the active metal method to manufacture a circuit board according to a comparative example.

When the maximum deflection and bending strength of the circuit boards according to Examples 1 to 3 and the comparative example thus prepared were measured, the silicon nitride circuit boards 1 according to Examples 1 to 3 were It was found that the maximum deflection amount and bending strength were at least twice as high as the circuit board of the comparative example using the aluminum nitride substrate. It was also confirmed that as the thickness of the silicon nitride substrate was reduced, the amount of deflection and the bending strength were further improved. Further, it was confirmed that the thermal resistance is reduced due to the reduction of the board thickness, so that the heat dissipation characteristics of the entire circuit board can be further improved.

When the circuit board of each of the above-described embodiments was mounted on the board in the assembly process, tightening cracks did not occur, and semiconductor devices using the circuit board could be mass-produced with a high manufacturing yield. In addition, a plurality of semiconductor elements 6, 6
Are collectively mounted on the same silicon nitride substrate 2, so that the circuit substrate can be made compact as compared with the case where the circuit substrate is individually formed for each semiconductor element, and the device for the circuit substrate is also provided. The number of integrations into the product has also been reduced, and the mountability has been greatly improved.

Each circuit board is heated from −45 ° C. to room temperature (RT), then heated from room temperature to + 125 ° C., and then cooled again to −45 ° C. through room temperature, which is one cycle. A cycle was repeatedly added and a heat-resistant cycle test was conducted to measure the number of cycles until a crack or the like was generated in the substrate part. With the circuit boards of Examples 1 to 3, even after 1000 cycles, Si ₃ N ₄ Board cracks and metal circuit boards (Cu circuit boards)
It was found that no peeling was observed and the excellent heat cycle characteristics were exhibited. On the other hand, in the circuit board of the comparative example, 1
It was confirmed that cracks occurred at 00 cycles and the durability was low.

As shown in FIG. 1, the grooves 10 having a V-shaped cross section are preliminarily formed in the back copper plate 5 at intervals so that the expansion and contraction of the back copper plate 5 during the heat cycle can be absorbed to some extent. It will be possible. Therefore, even when the large-sized circuit board 1 is formed by using the wide-area silicon nitride substrate 2 for mounting the plurality of elements 6, the thermal stress due to the heat cycle is small and the circuit board 1
There is little occurrence of warpage.

Example 4 The Si ₃ N ₄ substrate prepared in Examples 1 to 3 has a thermal conductivity k of 92 W / m · K and a thickness of 0.4.
By heating each Si ₃ N ₄ substrate having a size of 0.6 mm, 0.6 mm, and 0.8 mm in an oxidation furnace at a temperature of 1300 ° C. for 12 hours,
The entire surface of the substrate was oxidized to form an oxide layer having a thickness of 2 μm. The oxide layer is formed of a SiO ₂ film.

Next, a copper circuit board made of tough pitch electrolytic copper having a thickness of 0.3 mm is placed in contact with the surface side of each Si ₃ N ₄ substrate on which an oxide layer has been formed, while a tough pitch of 0.25 mm thickness is provided on the back side. A copper circuit board made of copper is placed as a backing material in contact with each other to form a laminated body, and the laminated body is inserted into a heating furnace adjusted to a nitrogen gas atmosphere at a temperature of 1075 ° C. and heated for 1 minute to obtain each Si ₃ N 2. Si _{3 in} which copper circuit boards are directly bonded to both sides of ₄ boards, and two semiconductor elements are solder bonded
N ₄ circuit boards were prepared respectively.

[0083] Each Si ₃ N ₄ circuit board 1a is oxidized layer 3 made of SiO ₂ is formed on the entire surface the Si ₃ N ₄ substrate 2 as shown in FIG. 2, Si ₃ N ₄ surface of the substrate 2 While the copper circuit board 4 as a metal circuit board is directly joined to the side,
Similarly, a copper circuit board 5 as a back copper board is directly joined to the back side, and semiconductor elements 6 are integrally joined to two predetermined positions of the copper circuit board 4 on the front side via solder layers not shown. Have. When the copper circuit boards 4 and 5 are bonded to both surfaces of the Si ₃ N ₄ substrate 2, the copper circuit board 5 as the back copper plate contributes to promotion of heat dissipation and prevention of warpage, which is effective.

The maximum deflection of the Si ₃ N ₄ circuit board according to Example 4 in which the circuit layer was formed by the direct bonding method as described above was in the range of 0.7 to 1.6 mm, and the bending strength was 550. It was in the range of up to 900 MPa, and a characteristic value equivalent to that when the circuit layer was formed by the active metal method as in Examples 1 to 3 was obtained. Further, in the heat resistance cycle test, there was no cracking of the Si ₃ N ₄ substrate or peeling of the metal circuit board even after 1000 cycles, and excellent heat resistance cycle characteristics were exhibited.

Example 5 As shown in FIG. 3, Si prepared in Examples 1 to 3
Si that is a ₃ N ₄ substrate and has a thermal conductivity k of 92 W / m · K and a thickness of 0.4 mm, 0.6 mm, and 0.8 mm, respectively.
_On the surface of the ₃ N ₄ substrate 2, a mixed powder of molybdenum (Mo) and titanium oxide (TiO ₂ ) to which a suitable amount of a binder and a solvent was added to form a paste was screen-printed and heated to a thickness. High melting point metal materization layer 8 of 15 μm
Was formed. Further, a Ni plating layer 9 having a thickness of 3 μm was formed on the metallized layer 8 by an electroless plating method to form a circuit layer having a predetermined pattern. Next, the semiconductor element 6 was joined to the two places on the circuit layer by soldering to manufacture many silicon nitride circuit boards 1b according to the fifth embodiment.

The maximum amount of deflection of the Si ₃ N ₄ circuit board according to Example 5 in which the circuit layer was formed by the metallizing method as described above was in the range of 1.0 to 1.8 mm, and the bending strength was 650 to 650. It was in the range of 950 MPa, and a characteristic value equivalent to that when the circuit layer was formed by the active metal method as in Examples 1 to 3 was obtained. In the heat resistance cycle test, 1000
There was no cracking of the Si ₃ N ₄ substrate or peeling of the circuit layer (metallized layer) 8 even after the lapse of cycles, and the circuit substrate subjected to the plating treatment also showed excellent heat resistance cycle characteristics.

Next, an embodiment of a circuit board using another silicon nitride substrate having various compositions and characteristic values will be specifically described with reference to Example 6 shown below.

Example 6 First, various silicon nitride substrates as constituent materials of a circuit board were manufactured by the following procedure.

That is, a silicon nitride raw material powder having an average particle diameter of 0.55 μm, containing 1.3% by weight of oxygen, 0.15% by weight of the impurity cation elements in total, and 97% of α-phase type silicon nitride. On the other hand, as shown in Tables 1 to ₃ , rare earth oxides such as Y ₂ O ₃ and Ho ₂ O ₃ as sintering aids,
If necessary, Ti, Hf compound, Al ₂ O ₃ powder, Al
N powder was added, and the mixture was wet-mixed in ethyl alcohol for 72 hours using a silicon nitride ball and then dried to prepare raw material powder mixtures. Next, a predetermined amount of an organic binder was added to each of the obtained raw material powder mixtures and uniformly mixed, followed by press molding at a molding pressure of 1000 kg / cm ² .
Many molded articles having various compositions were manufactured. Next, after degreasing each of the obtained compacts in an atmospheric gas at 700 ° C. for 2 hours, the degreased compacts were densified and sintered under the sintering conditions shown in Tables 1 to 3, and then attached to a sintering furnace. The cooling rate of the sintered body until the temperature inside the sintering furnace drops to 1500 ° C. by controlling the amount of electricity supplied to the heating device
The sintered body was cooled by adjusting it to the value shown in No. 3, and the silicon nitride sintered bodies of Samples 1 to 51 were prepared.

The average values of porosity, thermal conductivity (25 ° C.), and three-point bending strength at room temperature were measured for each of the silicon nitride sintered bodies of Samples 1 to 51 thus obtained. Further, the ratio (area ratio) of the crystal phase in the grain boundary phase was measured for each sintered body by the X-ray diffraction method, and the results shown in Tables 1 to 3 below were obtained.

[0091]

[Table 1]

[0092]

[Table 2]

[0093]

[Table 3]

As is clear from the results shown in Tables 1 to 3, in the silicon nitride sintered bodies according to Samples 1 to 51, the raw material composition was appropriately controlled, and immediately after the densification and sintering was completed as compared with the conventional example. Since the cooling rate of the sintered body is set lower than before, the higher the ratio of the crystal phase in the grain boundary phase and the higher the proportion of the crystal phase, the higher the heat dissipation and the high strength silicon nitride sintered body with high heat dissipation. was gotten.

On the other hand, 1.3 to 1.5% by weight of oxygen and 0.13 to 0.1% by weight of the above impurity cation elements are included.
A silicon nitride raw material powder containing 6% by weight and containing 93% of α-phase type silicon nitride and having an average particle size of 0.60 μm was used, and 3% of Y ₂ O ₃ (yttrium oxide) powder was added to the silicon nitride powder. ~ 6 wt% and 1.3-1.6 wt% alumina powder
The added raw material powder is molded and degreased, then sintered at 1900 ° C. for 6 hours and cooled in a furnace (cooling rate: 400 ° C./hour). The thermal conductivity was close to that of the silicon nitride sintered body manufactured by the conventional general manufacturing method.

Next, by polishing each of the obtained silicon nitride sintered bodies according to Samples 1 to 51, the thickness of 0.4 mm, 0.6 mm and 0.8 mm was obtained in the same manner as in Examples 1 to 5. Each silicon nitride substrate was prepared. Next, according to Example 6 as shown in FIG. 1, a copper circuit board or the like is integrally bonded to the surface of each silicon nitride substrate prepared by using the active metal method as in Examples 1 to 3. Each silicon nitride circuit board was prepared.

In addition, Example 4 was formed on the surface of each silicon nitride substrate.
By directly joining a copper circuit board and the like using the DBC method in the same manner as in, a silicon nitride circuit board according to Example 6 as shown in FIG. 2 was prepared.

Further, by forming a circuit layer on the surface of each silicon nitride substrate by using the metallizing method as in the fifth embodiment, the silicon nitride circuit substrate according to the sixth embodiment as shown in FIG. 3 is obtained. Each was prepared.

Each S according to the sixth embodiment in which the circuit layer is formed by the active metal method, the DBC method, and the metallizing method as described above.
The maximum deflection amount and bending strength of the i ₃ N ₄ circuit board are shown in Example 1.
5 or more, and there was no cracking of the Si ₃ N ₄ substrate or peeling of the circuit layer even after 1000 cycles in the heat resistance cycle test, and excellent heat resistance cycle characteristics were obtained.

[0100]

As described above, according to the silicon nitride circuit board of the present invention, in addition to the high strength and high toughness characteristic inherent to the silicon nitride sintered body, the thermal conductivity is greatly improved. A circuit layer is integrally bonded to the surface of a silicon nitride substrate having high thermal conductivity, and a plurality of semiconductor elements are mounted on the circuit layer. Therefore, even when the circuit board is formed in a large size to mount a plurality of elements, the toughness value is high, so that a large maximum deflection amount can be secured. for that reason,
It is possible to mass-produce a semiconductor device using a circuit board with a high manufacturing yield without causing a tightening crack of the circuit board in the assembly process.

Further, since a plurality of semiconductor elements are mounted on the surface of one silicon nitride substrate to form a circuit board, compared to the conventional case where a circuit board is formed for each semiconductor element, It is possible to reduce the total number of circuit boards, simplify the circuit board mounting process, and improve the manufacturing efficiency of semiconductor devices.

Further, since the toughness value of the silicon nitride substrate is high,
It is possible to provide a semiconductor device in which cracks are less likely to occur in a substrate due to heat cycle, heat cycle characteristics are remarkably improved, and durability and reliability are excellent.

Further, since a silicon nitride substrate having a high thermal conductivity, which has not been achieved in the past, is used, even when a semiconductor element aiming at high output and high integration is mounted, the thermal resistance characteristic is improved. Shows excellent heat dissipation with little deterioration.

In particular, since the silicon nitride substrate itself is excellent in mechanical strength, when the required mechanical strength characteristics are kept constant, the substrate thickness can be made larger than that when other ceramic substrates are used. It becomes possible to reduce. Since the substrate thickness can be reduced, the thermal resistance value can be made smaller,
The heat dissipation characteristics can be further improved. Further, since it is possible to sufficiently meet the required mechanical characteristics even with a substrate thinner than before, it is possible to mount the circuit board at a high density and further downsize the semiconductor device.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a silicon nitride circuit board according to the present invention.

FIG. 2 is a sectional view showing another embodiment of the silicon nitride circuit board according to the present invention.

FIG. 3 is a sectional view of a circuit board on which a circuit layer is formed by a metallizing method.

[Explanation of symbols]

1, 1a, 1b Silicon nitride circuit board (Si ₃ N ₄ circuit board) 2 Silicon nitride (Si ₃ N ₄ ) board 3 Oxide layer (SiO ₂ film) 4 Metal circuit board (Cu circuit board), Circuit layer 5 Metal circuit board (back copper plate) 6 Semiconductor element (chip) 7a, 7b Active metal brazing material layer 8 Refractory metal metallization layer 9 Metal plating layer (Ni plating layer) 10 Groove

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mitsuyasu Komatsu 4-4 shares, 2 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Toshiba Keihin Office (72) Inventor Nobuyuki Mizutani 4 shares, 2 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Company Toshiba Keihin Office

Claims (9)

[Claims] 1. A rare earth element converted into an oxide of 2.0 to 2.0.
17.5 wt%, Li, N as impurity cation element
a, K, Fe, Ca, Mg, Sr, Ba, Mn, and B are contained in a total amount of 0.3 wt% or less, and the thermal conductivity is 60 W / m.
A circuit board in which a circuit layer is bonded to a high-thermal-conductivity silicon nitride substrate having a temperature of K or more, wherein a plurality of semiconductor elements are mounted on the high-thermal-conductivity silicon nitride substrate via the circuit layer. Silicon circuit board. 2. A rare earth element converted into an oxide of 2.0 to.
17.5 wt%, Li, N as impurity cation element
a, K, Fe, Ca, Mg, Sr, Ba, Mn, and B in a total amount of 0.3 wt% or less, and is composed of a silicon nitride crystal and a grain boundary phase, and a grain of a crystalline compound phase in the grain boundary phase. A circuit board in which a circuit layer is bonded to a high thermal conductivity silicon nitride substrate having a ratio of 20% or more with respect to the entire phase and a thermal conductivity of 60 W / mK or more, and the high thermal conductivity silicon nitride substrate. A silicon nitride circuit board having a plurality of semiconductor elements mounted thereon via a circuit layer. 3. A high-thermal-conductivity silicon nitride substrate is composed of silicon nitride crystals and a grain boundary phase, and the ratio of the crystal compound phase in the grain boundary phase to the whole grain boundary phase is 50% or more. The silicon nitride circuit board according to claim 2, wherein the silicon nitride circuit board comprises a body. 4. The three-point bending strength of the high thermal conductivity silicon nitride substrate is 650 MPa or more.
The described silicon nitride circuit board. 5. The silicon nitride circuit board according to claim 1, wherein the thickness of the high thermal conductive silicon nitride board is not more than twice the thickness of the circuit layer. 6. The silicon nitride circuit board according to claim 1, wherein the high thermal conductivity silicon nitride substrate has a thermal conductivity of 90 W / m · K or more. 7. The silicon nitride according to claim 1, wherein the circuit layer is a metal circuit board, and the metal circuit board is bonded onto a high thermal conductive silicon nitride substrate having an oxide layer on the surface thereof. Elementary circuit board. 8. The circuit layer is a metal circuit board, Ti, Z
The metal circuit board is bonded onto a high thermal conductivity silicon nitride substrate through an active metal brazing material layer containing at least one active metal selected from r, Hf and Nb. Item 1. A silicon nitride circuit board according to item 1. 9. The silicon nitride circuit board according to claim 1, wherein the circuit layer comprises a refractory metallized layer.